Unsaturated Penta-Coordinated Mo_5c⁵⁺ Sites Enabled Low-Temperature Oxidation of C-H Bonds in Ethers

Selective oxidation of C-H bonds under mild conditions is one of the most important and challenging issues in utilization of energy-related molecules. Molybdenum oxide nanostructures containing Mo⁵⁺ species are effective for these reactions, but the accurate identification of the structure of active Mo⁵⁺ species and the catalytic mechanism remain unclear. Herein, unsaturated penta-coordinated Mo_5c⁵⁺ with a high fraction in MoO fabricated by the hydrothermal method were identified as the active sites for low-temperature oxidation of dimethyl ether (DME) by the deep correlation of characterizations, density functional theory calculations, and activity results, giving a methyl formate selectivity of 96.3% and DME conversion of 12.5% at unreported 110 °C. Low-temperature electron spin resonance (ESR) and quasi in situ X-ray photoelectron spectra (XPS) with the designed experiments confirm that the Mo_5c⁵⁺ species can be formed in situ. Molybdenum located at the pentachronic site is preferable to significantly promote the oxidation of the C-H bond in CH₃O* at lower temperatures.